Yuichiro Shimoyanagi works as a 3D director at Musashino Animation and shares a long-standing friendship with animator Ryosuke Endo, forged through their mutual mentorship under Saburou Kitano and shared passion for the anime *Space Exodus Idepon*.

During *Exodus!* production, a communication failure involving production assistant Tarou Takanashi drives Endo to quit in frustration. Shimoyanagi later joins Endo, Takanashi, and production assistant Aoi Miyamori at an *Idepon* exhibition, where he and Endo reconcile and acknowledge each other's talents.

After *Time Hippopotamus* cancels, Shimoyanagi leaves Musashino Animation but eventually returns. He becomes pivotal in *Air Amphibious Assault Ship SIVA*'s production by spearheading efforts to recruit Endo back into animation following Endo's demoralization over *Time Hippopotamus*. With Misato Segawa, Shimoyanagi approaches Endo, and bolstered by encouragement from Endo's wife Mayumi, they successfully persuade him to join the project.